The present invention relates to a communication terminal and a communication server used for people to talk with one another mainly in voice through a medium.
A first conventional technique relating to the present invention is FreeWalk, which is a conference system developed by Kyoto University. See, for example, NAKANISHI, Hideyuki, YOSHIDA, Chikara, NISHIMURA, Toshikazu, and ISHIDA, Toru, “FreeWalk: Support of Non-formal Communication Using Three-dimensional Virtual Space”, IPSJ Journal, Vol. 39, No. 5, pp. 1356–1364, 1998 (hereinafter, referred to as Non-patent Documents 1) and Nakanishi, H., Yoshida, C., Nishimura, T., and Ishida, T., “FreeWalk: A 3D Virtual Space for Casual Meetings”, IEEE MultiMedia, April–June 1999, pp. 2028 (hereinafter, referred to as Non-patent Documents 2). FreeWalk is a system in which users of the conference system share a virtual space and users in the same space can talk with one another. Each user can see this virtual space by three-dimensional graphics, as an image seen from his viewpoint or from a viewpoint that is near to his viewpoint but able to see himself within the range of vision. Three-dimensional graphics is a technique for simulating a three-dimensional space by computer graphics, and, for example, OpenGL (http://www.opengl.org/), which is de facto standard, and Direct 3D of Microsoft Corporation are APIs (Application Programming Interface) for achieving that end. An image of a conversational partner is shot by a video camera and projected in real time on a virtual screen located in the image seen from, for example, the user's viewpoint. Further, each user can move free in this virtual space. Namely, each user can change his location in this virtual space, using a pointing device or keys of a keyboard. In Non-patent documents 1 and 2, voice is damped as distance increases, but those documents do not mention the below-mentioned three-dimensional audio technique.
A second conventional technique relating to the present invention is Somewire, which is a conference system developed by Interval Research Corporation. See, for example, U.S. Pat. No. 5,889,843 (hereinafter, referred to as Patent Documents 1), U.S. Pat. No. 6,262,711 B1 (hereinafter, referred to as Patent Documents 2), and Singer, A., Hindus, D., Stifelman, L., and White, S., “Tangible Progress: Less Is More In Somewire Audio Spaces”, ACM CHI '99 (Conference on Human Factors in Computing Systems), pp. 104 to 112, May 1999 (hereinafter, referred to as Non-patent Document 3). Somewire is a system in which users of the conference system share a virtual system and users in the same space can talk with one another. In Somewire, voice is reproduced by high quality stereo audio. Further, Somewire has an intuitive tangible interface, since it employs GUI (Graphical User Interface) that can control a location of a conversational partner in the virtual space by moving a doll-like figure. In Somewire, voice is not damped as distance increases, and the three-dimensional audio technique is not employed.
A third conventional technique relating to the present invention is a conference system using the distributed 3D audio technique developed by Hewlett-Packard Company. See, for example, Low, C. and Babarit, L., “Distributed 3D Audio Rendering”, 7th International World Wide Web Conference (WWW7), 1998, http://www7.scu.edu.au/programme/fullpapers/1912/com1912.htm (hereinafter, referred to as Non-patent Document 4). The distributed 3D audio technique is a technique that applies the three-dimensional audio technique to a networked system (so-called distributed environment). The three-dimensional audio technique is a technique of simulating a three-dimensional acoustic space, and, for example, Open AL (http ://www.opengl.org/) prescribed by Loki Entertainment Software Inc. and others and DirectSound 3D of Microsoft Corporation, EAX2.0 (http://www.sei.com/algorithms/eax20.pdf) of Creative Technology, Ltd. are mentioned as API for achieving that end. Using the three-dimensional audio technique, it is possible to simulate a direction and distance of a sound source seen from a listener, in sound reproduction using speakers such as headphones or 2- or 4-channel speakers, and to locate the sound source in an acoustic space. Further, by simulating acoustic properties such as reverberation, reflection by an object such as a wall, sound absorption by air depending on distance, sound interception by an obstacle, and the like, it is possible to express an impression of existence of a room and an impression of existence of an object in a space. The three-dimensional audio technique is one of stereo phone reproduction systems. In addition to the three-dimensional audio technique, stereo phone reproduction systems include simple stereo phone reproduction techniques. For example, may be mentioned a stereo phone reproduction technique that differentiates sound volumes between left and right speakers in headphones to reproduce a plurality of sounds separately.